Whip butter and sugars until fluffy, about 3 minutes. Add 1 egg and vanilla, mix until combined. Combine all dry ingredients in a bowl, set aside. Combine bananas and buttermilk in bowl, set aside. Add banana mixture into butter mixture, alternating with dry mixture. Do this in 2-3 turns until well combined. Pipe out batter onto tray about 1 1/4 inch dollops, keep cakes at least 1 1/2 apart (more if possible). Bake for 12-14 minutes until golden.